Oil and gas well operation fluid used for the solvation of waxes and asphaltenes, and method of use thereof

ABSTRACT

A wax and asphaltene solvation fluid for use in oil and gas wells is derived as a residual fluid from a feedstock that includes a greater mass percentage of trimethylbenzene than decane, and is preferably sour. Mass percentage of both aromatics and asphaltenes in the residual fluid is in the 30%-70% range, and a complex mixture of both is described.

This application is a continuation of application Ser. No. 08/195,993, filed Feb. 14, 1994 now abandoned.

FIELD OF THE INVENTION

This invention relates to oil and gas well operation fluids, particularly those used for the removal of contaminants from wells.

BACKGROUND AND SUMMARY OF THE INVENTION

The rocks that contain oil and gas in oil and gas reservoirs are porous and to remove the oil or gas from the reservoirs requires that the oil or gas move through the pores in the rock. If the pores are blocked, then it is difficult and it may even become impossible to remove the oil or gas from the reservoir, with consequent economic loss to the oil or gas well owner.

Two notorious contaminants that may block the pores are waxes and asphaltenes. A wax is normally defined as a hydrocarbon that is a solid at room temperature and has 20 carbon atoms or more. An asphaltene is an agglomerate of aromatic hydrocarbons, and may contain bound oxygen, nitrogen and sulphur atoms. The oil and gas in many, if not most, reservoirs contains both waxes and asphaltenes. These waxes and asphaltenes may be dissolved in the oil. In some cases, however, the waxes and asphaltenes may partially block the pores, or, as production continues, the very action of removing oil from a reservoir may cause waxes and asphaltenes to precipitate out of solution and block the pores.

Also, the waxes and asphaltenes may precipitate out of solution in the well bore itself, or in equipment used for the production of oil and gas and reduce or block the flow of oil from the well.

The economic damage from waxes and asphaltene precipitation can be very high, killing some wells entirely. Consequently, a great deal of attention has been devoted to developing cost effective ways of preventing waxes and asphaltenes from precipitating out of solution or of removing the waxes and asphaltenes from an oil reservoir or well bore.

One such attempt at a solution has been to apply to a well a mixture of a significant proportion of the aromatic xylene (about 45%) and a lesser proportion of the paraffinic hydrocarbon hexane (about 30%), together with about 25% methanol. This product is known by the name NP760 and is available from Wellchem of Calgary, Alberta, Canada. The xylene is intended to solvate asphaltenes and the hexane is intended to solvate waxes. The xylene and hexane components of the composition are each derived from refining a feedstock and removing that particular component from the feedstock. The result is a product that has moderate success in solvating at least some waxes and asphaltenes, but because the fluid is made from a complex process, the fluid is relatively expensive.

One difficulty with the use of hexane or other alkanes is that they tend to cause asphaltenes to precipitate out of solution. This in turn is believed to increase the precipitation of waxes. How this is believed to occur is as follows. Waxes require nucleation sites in the oil formation or well bore to which they can attach. Any such site will become a nucleation site for the further accretion of waxes. In time, the waxes, mixed with asphaltenes, build outward and block the well bore or pores in the formation. In a typical oil formation water surrounds the rock in the formation and waxes will tend to slide off the water and not attach to the rock. However, if asphaltenes are present, they may attach to the rock surface since reservoir rock contains positively and negatively charged molecules (cations and anions) which attract the polar asphaltenes. The asphaltenes may then protrude beyond the water layer surrounding the rock particle and form a nucleation site for waxes. Hence a precondition for wax deposition is the precipitation of asphaltenes from the oil in the reservoir. It is the hexane that causes the precipitation of the asphaltenes and thus the formation of nucleation sites for waxes. The xylene is added to solvate the asphaltenes and prevent the formation of nucleation sites.

However, such a product, formed of an alkane (particularly pentane, hexane and heptane) and an aromatic, and similar products that are produced by the steps of: (a) refining a feedstock, (b) selectively removing hydrocarbons and (c) subsequently mixing the selected hydrocarbons, are not believed very effective in removing gummy layers of waxes and asphaltenes that are typically found in oil and gas reservoirs and well bores in relation to their cost. The waxy depositions in oil and gas formations are complex aggregations of molecules, with many layers and globules of different waxes and asphaltenes, which the inventors have found are not readily removed by simple compositions. Such products, requiring several processing steps, tend to be expensive. Also, in some wells such mixtures of an aromatic, alkane and alcohol or other polar substance may increase the precipitation of waxes and asphaltenes. Thus for example, in the general case, stabilized C₅ + condensates tend to precipitate asphaltenes, with the future risk of wax contamination for the reasons just mentioned. That is to say, while it is possible to tailor a particular composition of alkanes and aromatics to a particular well formation, such a procedure is relatively expensive and may produce a product that is useful for one well formation but not for another. With the expense of the product and the risk of actually damaging the well, the application of such a product to a well is a venture not lightly undertaken.

The inventors have found a composition and a method for its use that helps to remove the uncertainty from applying wax solvating materials to wells, while at the same time significantly reducing the cost of making and using the composition. The composition is formed from a complex mixture of aromatics and alkanes (preferably C₇ +). The complex mixture provides different components that solvate different waxes and asphaltenes. Rather than using a composition derived from selecting individual components during refining, the composition is the residue after lighter hydrocarbon components (preferably substantially all C₁, C₂, C₃, C₄ and C₅ hydrocarbons) have been removed during refining. With the appropriate selection of the feedstock, an improved wax solvating and asphaltene solvating composition may be derived.

The feedstock should be selected to have a significant proportion of aromatics and alkanes. The inventors have found that if a feedstock has a mass percentage of trimethylbenzene higher than the mass percentage of n-decane as determined by gas chromatography then the feedstock will have a sufficiently complex mixture of aromatics and alkanes for the efficient solvating of asphaltenes and waxes, particularly after the lighter ends (C₁, C₂, C₃, C₄ and C₅ hydrocarbons) have been removed by distillation from the feedstock. By a sufficiently complex mixture of aromatics is meant aromatics other than the simple aromatics benzene, toluene, ethylbenzene and xylene. These simple aromatics are the aromatics normally measured in gas chromatography since they usually yield well defined peaks. The inventors have found that it is necessary to have a good quantity of other aromatics, and the presence of these other aromatics is indicated by the quantity of trimethylbenzene.

Another indication that a feedstock contains a suitably complex blend of aromatics and alkanes to solvate complex gummy layers of waxes and asphaltenes is the presence of sulphur containing compounds in the feedstock. It is believed that sulphur is a catalyst for the conversion of alkanes to aromatics during the many years that the hydrocarbon deposit evolves underground. Hence, the more sulphur, the greater the conversion of alkanes to aromatics. Thus the presence of sulphur is an indication that the feedstock will have a suitable proportion of aromatics to alkanes.

Aromatic composition and alkane composition should be in the range 30% to 70% by mass percentage as determined by gas chromatography for a suitable composition. However, it is not believed that such a range of aromatics and alkanes is sufficient: the composition must be suitably complex as noted above. Further, it has been found desirable that the feedstock be clear or have a light colour such as amber. Dark colour indicates the presence of heavy ends (C₁₆ +) that assist in the formation of waxes. The C₁₆ + content of the fluid should preferably be below 2% by mass as determined by gas chromatography. If the feedstock contains greater than 2% C₁₆ + content, then an additional cut may be taken to remove all or substantially all the higher ends.

Alternatively, the fluid may be formulated for pure asphaltene solvation. Pure asphaltene generally occurs in only two situations in the reservoir. In one case, pyrobitumen can be present in gas reservoirs. This is generally believed to have been deposited long ago when oil which had occupied the reservoir migrated out and left the pyrobitumen behind. This pyrobitumen can move during production and plug the formation or wellbore.

Another case is in tertiary recovery using hydrocarbon miscible solvents floods. Light hydrocarbons in the C₂ to C₅ range are injected into the reservoir to push the oil to production wells. While these light hydrocarbons will solvate paraffinic molecules they act to precipitate asphaltenic molecules. Thus asphaltene will precipitate without heavy paraffinic molecules present.

The fluid is formulated for solvating pure asphaltenes by increasing the temperature of the cutpoint. This removes the C₆ and C₇ components which contain a lower percentage of aromatics than the bulk residue. The aromatics in this region are small and not as effective as the more complex aromatics in the remainder of the fluid.

Asphaltenes are normally colloidally suspended in crude oil by peptizing resins (maltenes). These peptizing resins are aromatic and polar at one end and paraffinic or neutral at the other end. The polar end is attracted to the asphaltene and the nonpolar end to the crude oil. When the solid asphaltene is completely surrounded by peptizing resins it becomes a colloidally suspended particle completely suspended in the crude oil.

Currently the main way of treating these precipitations is by injecting pure xylene down a well. Xylene is a simple aromatic with short paraffinic side chains. The more complex aromatics in the C₈ + fluid described here with longer side chains provide superior emulation of the maltenes that originally suspended the asphaltene molecules than just pure xylene.

DESCRIPTION OF THE DRAWINGS

The present invention will be better understood in conjuction with the appended drawings in which:

FIG. 1 is a gas chromatograph profile of a C₅ + feed from the Wildcat Hills Plant in Alberta, Canada, which is a preferrred composition of the present invention;

FIG. 2 is a gas chromatograph profile of a C₅ + feed from the Jumping Pound Plant in Alberta, Canada, which is an alternate preferred composition of the present invention;

FIG. 3 is a gas chromatograph profile of a feedstock from the Shell Caroline Gas Plant in Alberta, Canada, which is an alternate preferred composition of the present invention; and FIG. 4 is a gas chromatograph profile of a feed stock from the Hanlan Gas Plant in Alberta, Canada, which is another alternate preferred composition of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

As used in this present application: a residual fluid is a fluid that remains after light hydrocarbon components (particularly C₁, C₂, C₃, C₄ and C₅ components) of a hydrocarbon feedstock are removed during the refining of the hydrocarbon feedstock; a hydrocarbon feedstock is a hydrocarbon fluid that has been produced directly from an oil or gas bearing formation; sour means sulphur containing. C_(n) + indicates no greater than a small percentage (less than 5%) of C₁, C₂, . . . C_(n-1).

The preferred composition is a residual hydrocarbon fluid derived from a hydrocarbon feedstock having a complex mixture of aromatics. Complex in this context means that there are included in the mixture aromatics other than benzene, toluene, ethylbenzene and xylene, such as methylethylbenzene, diethylbenzene and propylethylbenzene, to name but a few of the possibilities. The hydrocarbon feedstock from which the fluid according to the invention is derived should contain a greater percentage of trimethylbenzene than n-decane, in which case it is believed that the fluid will have the desirable wax and asphaltene solvating properties. It should be noted that these aromatics, other than benzene, toluene, ethylbenzene and xylene, are not readily identifiable using gas chromatography, and so having the trimethylbenzene peak higher than n-decane is the manner in which the appropriate feedstock may be identified. According to one aspect of the invention, the feedstock is preferably but not necessarily refined to remove essentially all C₁, C₂, C₃, C₄ and C₅ hydrocarbons components. It is not necessary that the feedstock have a relatively low ratio of alkanes if the alkanes are concentrated in the lighter ends and the lighter ends are removed by distillation. The feedstock is preferably sour and clear or light amber, with sulphur content exceeding 1500 ppm, and preferably has no more than about 2% C₁₆ +. In general it is believed that the more sulphonated the feedstock, the better for asphaltene salvation. If the C₁₆ + content is greater than 2%, a further cut should preferably be taken to remove the higher ends.

FIGS. 1 and 2 are gas chromatographic profiles (graphic and numerical) of preferred compositions of the feedstock from which the fluid according to the invention may be derived. FIG. 1 is a gas chromatograph profile of the C₅ + feed from the Wildcat Hills plant in Alberta, Canada. FIG. 2 is a gas chromatograph profile of the C₅ + feed from the Jumping Pound plant in Alberta, Canada. The trimethylbenzene marker is indicated at 10 and the n-decane marker is indicated at 12 in each FIGURE. Tables 1 and 2 are numerical representations of the chromatographs of FIGS. 1 and 2, respectively.

                  TABLE 1                                                          ______________________________________                                         WILDCAT HILLS                                                                  RT        AREA %         NAME                                                  ______________________________________                                          3.202    .07508         iC4                                                    3.912    .35699         nC4                                                    5.784    2.69133        iC5                                                    6.514    2.72246        nC5                                                    7.492    .67313         Cyclopentane                                           8.340    .89997                                                                8.487    3.99820                                                               8.875    2.17882                                                               9.377    6.74750        C6                                                    10.097    2.47707        Methyl cyclopentane                                   10.340    .08951                                                               10.752    3.93949        Benzene                                               10.887    .18034                                                               11.012    2.71677        Cyclohexane                                           11.201    2.88368                                                              11.428    2.21393                                                              11.641    .47199                                                               11.774    1.38668                                                              12.062    4.72465        C7                                                    12.688    6.65060        Methyl cyclohexane                                    12.910    .72919                                                               13.125    .22715                                                               13.313    .18384                                                               13.554    12.71929       Toluene                                               13.710    2.10055                                                              13.900    1.04831                                                              14.090    1.44920                                                              14.287    .47715                                                               14.505    3.13432        C8                                                    14.716    .17785                                                               14.970    .09517                                                               15.048    .08244                                                               15.195    .49210                                                               15.370    .75489                                                               15.510    .46649                                                               15.759    .45354         m + p xylene                                          16.000    10.08547       m + p xylene                                          16.157    .54391                                                               16.504    1.51593        oxylene                                               16.615    .14003                                                               16.742    1.95847        C9                                                    17.068    .12964                                                               17.161    .14645                                                               17.366    .27271                                                               17.508    .58216                                                               17.822    .17800                                                               17.946    .79982                                                               18.105    1.68490                                                              18.245    .29447                                                               18.347    .13771                                                               18.493    .12346                                                               18.660    1.32512        trimethyl benzene                                     18.800    1.26158        C10                                                   18.965    .11433                                                               19.256    .53542                                                               19.382    .07666                                                               19.525    .11942                                                               19.616    .15763                                                               19.746    .13944                                                               19.856    .32040                                                               20.044    .31498                                                               20.180    .13753                                                               20.279    .10719                                                               20.420    .10568                                                               20.701    .94819         C11                                                   20.885    .15028                                                               21.060    .11153                                                               21.140    .11705                                                               21.250    .14451                                                               21.545    .19119                                                               21.732    .20552                                                               21.853    .13484                                                               21.980    .11113                                                               22.466    .63371         C12                                                   22.653    .05706                                                               22.740    .11454                                                               23.247    .06810                                                               23.367    .09962                                                               23.543    .12426                                                               23.749    .08606                                                               23.866    .06625                                                               24.119    .28868         C13                                                   24.306    .10446                                                               25.387    .05999                                                               25.668    .13514         C14                                                   27.125    .06827         C15                                                   ______________________________________                                    

                  TABLE 2                                                          ______________________________________                                         JUMPING POND                                                                   RT        AREA %         NAME                                                  ______________________________________                                          2.341    .97890                                                                2.618    .86497         C4                                                     2.816    .3861                                                                 3.697    14.33011       iC5                                                    4.236    10.12231       nC5                                                    5.066    .76730         Cyclopentene                                           5.784    .93620                                                                5.928    4.10632                                                               6.290    1.97614                                                               6.765    7.04991        iC6                                                    7.470    2.18292        Methyl cyclopentane                                    8.095    .89846         Benzene                                                8.240    .13707                                                                8.371    2.14099        Cyclohexane                                            8.551    2.20204                                                               8.995    1.54438                                                               8.775    .35825                                                                9.129    1.05C50                                                               9.421    3.83012        C7                                                    10.054    5.15676        Methyl cyclohexane                                    10.274    .55886                                                               10.488    .16983                                                               10.675    .13411                                                               10.904    5.37600        Toluene                                               11.082    1.53461                                                              11.277    .64754                                                               11.465    1.21631                                                              11.660    .25546                                                               11.739    .10947                                                               11.895    2.41510        C8                                                    12.101    .14885                                                               12.358    .07718                                                               12.588    .41137                                                               12.760    .53539                                                               12.899    .41128                                                               13.147    .27011         m + p xylene                                          13.399    6.57036        m + p xylene                                          13.560    .39226                                                               13.904    1.23017        oxylene                                               14.155    1.50142        C9                                                    14.471    .08211                                                               14.569    .10035                                                               14.774    .18688                                                               14.917    .40929                                                               15.237    .13187                                                               15.355    .50748                                                               15.520    1.27618                                                              15.663    .19968                                                               15.758    .09574                                                               15.909    .10972                                                               16.079    1.01203        trimethyl benzene                                     16.224    .96784         C10                                                   16.379    .08264                                                               16.674    .36803                                                               16.943    .07889                                                               17.033    .10599                                                               17.160    .08998                                                               17.275    .21482                                                               17.469    .23662                                                               17.602    .09868                                                               18.130    .64582         C11                                                   18.300    .09683                                                               18.485    .07766                                                               18.561    .08832                                                               18.669    .09555                                                               18.966    .12143                                                               19.155    .13286                                                               19.281    .11464                                                               19.405    .07735                                                               19.899    .48104         C12                                                   20.168    .07798                                                               20.974    .10136                                                               21.553    .25211         C13                                                   21.733    .08036                                                               23.105    .14083         C14                                                   24.563    .07604         C15                                                   ______________________________________                                    

To produce the formulation of the invention from the feedstocks shown in FIGS. 1 and 2, the feedstocks are refined to remove substantially all of the C₁, C₂, C₃, C₄ and C₅ hydrocarbons components, with a small percentage of C₆, C₇ and C₈ hydrocarbons.

With a 120° C. cut, the resulting fluid, as determined by gas chromatography, has about 0.1% pentane, 7% hexanes, 13% heptanes, 13% octanes, 7% nonanes, 9% decanes, 5% undecanes, 3% dodecanes, 2% tridecanes, 1% tetradecanes, 0.6% pentadecanes, 0.3% hexadecanes, 0.1% heptadecanes, 0.05% octadecanes, 1% benzene, 9% toluene, 12% ethyl benzene and meta- and para xylene, 2.6% ortho-xylene, 2.2% 1,2,4trimethylbenzene, 0.1% cyclopentane, 2% methylcyclopentane, 2.6% cyclohexane, 8% methylcyclohexane and less than 0.05% of any other constituent, including cumulatively less than 0.1% C₁₉ +. Naphthene content is greater than about 3%.

With a 130° C. cut, the resulting fluid, as determined by gas chromatography, has about 0% pentanes, 2% hexanes, 13% heptanes, 13% octanes, 7% nonanes, 9% decanes, 5% undecanes, 3% dodecanes, 2% tridecanes, 1% tetradecanes, 0.5% pentadecanes, 0.2% hexadecanes, 0.1% heptadecanes, 0.05% octadecanes, 1.5% benzene, 12.6% toluene, 15% ethyl benzene and meta- and para xylene, 2.4% ortho-xylene, 2.2% 1,2,4trimethylbenzene, 0% cyclopentanes, 1% methylcyclopentane, 1.9% cyclohexane, 7.8% methylcyclohexane and less than 0.05% of any other constituent, including cumulatively less than 0.1% C₁₉ +. It will be observed that with the higher cut, all of the remaining pentane, and more than 2/3 of the hexanes have been removed while the aromatic content has increased.

With a 140° C. cut, the resulting fluid, as determined by gas chromatography, has about 0% pentanes, 0.3% hexanes, 8.7% heptanes, 13.5% octanes, 6.7% nonanes, 10.7% decanes, 6% undecanes, 4% dodecanes, 2% tridecanes, 1% tetradecanes, 0.6% pentadecanes, 0.3% hexadecanes, 0.1% heptadecanes, 0.06% octadecanes, 0.6% benzene, 13.7% toluene, 17.9% ethyl benzene and meta- and para xylene, 2.7% ortho-xylene, 2.7% 1,2,4 trimethylbenzene, 0% cyclopentanes, 0.3% methylcyclopentane, 0.7% cyclohexane, 7% methylcyclohexane and less than 0.1% of any other constituent, including cumulatively less than 0.05% c₁₉ +.

With a 150° C. cut, the resulting fluid, as determined by gas chromatography, has about 0% pentanes, 0.01% hexanes, 2.5% heptanes, 14.4% octanes, 9.5% nonanes, 14.1% decanes, 8.1% undecanes, 5.2% dodecanes, 3.1% tridecanes, 1.8% tetradecanes, 1% pentadecanes, 0.4% hexadecanes, 0.2% heptadecanes, 0.1% octadecanes, 0.01% benzene, 8.3% toluene, 20.3% ethyl benzene and meta- and para xylene, 3.5% ortho-xylene, 3.5% 1,2,4 trimethylbenzene, 0% cyclopentane, 0% methylcyclopentane, 0.07% cyclohexane, 3.7% methylcyclohexane and less than 0.05% of any other constituent, including cumulatively less than 0.1% c₁₉ +.

With a 160° C. cut, the resulting fluid, as determined by gas chromatography, has about 0% pentanes, 0% hexanes, 0.2% heptanes, 7.9% octanes, 9.8% nonanes, 18.6% decanes, 10.8% undecanes, 6.9% dodecanes, 4.1% tridecanes, 2.3% tetradecanes, 1.2% pentadecanes, 0.5% hexadecanes, 0.2% heptadecanes, 0.1% octadecanes, 0% benzene, 2.2% toluene, 25.3% ethyl benzene and meta- and para xylene, 4.2% ortho-xylene, 5.0% 1,2,4 trimethylbenzene, 0% cyclopentane, 0% methylcyclopentane, 0% cyclohexane, 0.5% methylcyclohexane and less than 0.05% of any other constituent, including an undetectable amount of C₁₉ +.

For each of the 120° C., 130° C., 140° C., 150° C. and 160° C. cuts, all percentages are mass fraction. Only simple aromatics are identified. Supercritical fluid chromatography shows that the actual aromatic content is greater than 40%. For C₅ to C₁₈, the percentage given is the sum of the peaks from the gas chromatographic analysis. Thus, the figure for "decanes" includes the figure for straight chain decane. The higher cuts show increased percentages of C₈ and C₁₀, and increased xylene, particularly the 150° C. cut. The 130° C. cut is preferred for wax and asphaltene salvation. For the 120° C. cut, the fluid is amber in colour with a density of 780 kg/m³. Boiling point at 1 atm is 100°-300° C., freezing point about -60° C., vapour pressure <15 kpa, with a closed cup flash point of >10° C. As a flammable and toxic liquid, this fluid should be treated with well known safety precautions. At the higher cuts (150° C. cut), effectively all of the C₆ and C₇ is removed, with consequent increase in the xylene content to over 25%. Such a fluid is useful for pure asphaltene solvation.

Thus a preferred composition of the invention has less than 1% cumulatively of methane, ethane, propane, butane and pentane; 0 to 10% hexanes; 1 to 15% heptanes; 5 to 15% octanes; 5 to 15% nonanes; 5 to 15% decanes; 3 to 10% undecanes; 1 to 7% dodecanes; 0 to 5% tridecanes; 0 to 3% tetradecanes; 0 to 2% pentadecanes; 0 to 1% hexadecanes; 0 to 1% heptadecanes; 0 to 1% octadecanes; 0 to 3% benzene; 5 to 20% toluene; 10 to 35% xylenes; 1 to 5% 1,2,4trimethylbenzene; and cumulatively less than 2% C₁₆ +, all of the percentages being mass fraction as determined by gas chromatography. In another preferred composition according to the invention, the fluid includes less than 5% hexanes; 0 to 15% heptanes; 0 to 15% octanes; 5 to 15% nonanes; 5 to 25% decanes; 3 to 15% undecanes; 2 to 10% dodecanes; 0 to 5% tridecanes; 0 to 3% tetradecanes; 0 to 2% pentadecanes; 0 to 1% hexadecanes; 0 to 1% heptadecanes; 0 to 1% octadecanes; 0 to 3% benzene; 5 to 15% toluene; 15 to 40% xylenes; and 1 to 8% 1,2,4trimethylbenzene.

Solvation tests using the formulation according to the invention have yielded the following results.

                  TABLE 3                                                          ______________________________________                                         No.  Location      Solvent  Contaminant                                                                            % Dissolved                                ______________________________________                                          1.  08-20-044-04W5                                                                               #8       1.0284  86.8                                        2.  02-09-039-07  #8       0.9714  98.2                                        3.  02-20-039-07  #8       0.9959  97.0                                        4.  10-13 (Viking)                                                                               #8       1.0033  87.4                                        5.  06-10-035-06W4                                                                               #8       1.0280  96.2                                        6.  10-13 (Viking)                                                                                #10     0.9972  63.2                                        7.  06-10-035-06W4                                                                                #10     0.9547  64.2                                        8.  10-24-001-26  #8       1.0005  71.7                                        9.  8" Group Line #8       1.0004  68.6                                       10.  11-14-041-25  #8       1.0017  76.8                                       11.  08-14-041-25  #8       1.0567  98.5                                       12.  11-14-041-25  #9       1.0011  81.1                                       13.  08-14-041-25  #9       0.9987  97.2                                       14.  Utikuma Keg R.                                                                               #8       0.9536  63.0                                       15.  Utikuma Slave #8       1.0221  93.2                                       16.  Hutton 12-18  #8       1.0543  89.2                                       17.  10-18-048-08W5                                                                               #8       1.1200  97.8                                       18.  12-24-047-09 W4                                                                               #16     0.9756  99.3                                       19.  12C-19-036-04 #8       0.4624  87.3 @ 22° C.                       20.  16-01-004-21W3                                                                               #8       0.2992  75.2 @ 22° C.                       21.  Intensity Res.                                                                               #8       0.9845  97.1                                       22.  05-03-055-13W5                                                                               #8       0.9904  96.6                                       23.  16-14-055-13W5                                                                               #8       1.0509  21.4                                       23a. 16-14-055-13W5                                                                               Toluene  1.0458  *38.1                                      24.  Esso Wizard Lk.                                                                              90/10    0.9813  98.3                                       25.  Esso Wizard Lk.                                                                              #8       0.9940  96.6                                       26.  Esso Wizard Lk.                                                                              Run 95   1.0018  91.3                                       27.  Esso Wizard Lk.                                                                              90/10Xy  0.9726  97.0                                       28.  Esso Wizard Lk.                                                                              100Xy    0.9676  96.5                                       29.  16-03-040-04W5                                                                               #8       1.0485  84.5                                       30.  16-03-040-04W5                                                                               #9       1.0264  96.1                                       31.  046-09W5 Comaplex                                                                            #8       1.0545  76.1                                       32.  046-09W5 Comaplex                                                                            #9       0.9974  75.6                                       33.  07-11-053-26  #8       1.0292  97.9                                       34a. 16-19-071-04Chevron                                                                          #8       0.9756  94.4                                       34b. 02-06-072-04Chevron                                                                          #8       1.0014  98.7                                       34c. 16-19-071-04Chevron                                                                          100Xylene                                                                               0.9588  95.7                                       35.  02-06-072-04Chevron                                                                          100Xylene                                                                               1.4169  93.3                                       36.  Chauvco Unit No. 2                                                                           #8       0.9799  97.6                                       37.  06-10-035-03W5                                                                               #8       0.9548  66.5                                       38.  08-20-026-12W4                                                                               #8        1.10157                                                                               92.2                                       39.  03-13-044-09Amoco                                                                            #8       1.0397  82.9                                       40.  04-22-043-08Amoco                                                                            #8       0.9671  94.1                                       41.  02-05-043-08Amoco                                                                            #8       1.0202  93.8                                       42.  03-13-044-09Amoco                                                                            #9       0.9975  72.5                                       43.  04-22-043-08Amoco                                                                            #9       0.9760  96.1                                       44.  02-05-043-08Amoco                                                                            #9       1.0372  95.3                                       45.  Willesden Green                                                                              #8       1.0127  94.1                                       ______________________________________                                    

Notes to Table 3: Wax or asphaltene amount is listed in grams under the heading "contaminant". The origin of the sample contaminant is indicated by the location of the well, in the Province of Alberta, Canada, from which the sample was derived. % dissolved is the percentage of the original sample that was dissolved in the solvent. It is a general indicator of the effectiveness of the solvent on that particular composition of contaminant. The solvation testing procedure used to generate the data of Table 1 entailed the addition of the sample contaminant to the solvent being tested at ambient temperature, followed by stirring and chopping to maximize solvation, as a general indicator of the effectiveness of the solvent in actual well conditions. The ratio of solvent to contaminated sample was approximately 100 ml. to 1 gram. The amount of contaminated sample dissolved by the solvent was determined by filtering through a 1.5 micron filter. The amount of solvent used was 100 mL. #8 and #16 is the fluid described above as the 120° C. cut. #9 is a blend of NP760™ and 10% SUPER A SOL™, which is available from Petrolite Canada, Inc. of Calgary, Alberta, Canada. SUPER A SOL™ is a blended aromatic solvent and has the appearance of a clear colorless liquid, a density of 0.791 Kg per Liter at 15° C., a flash point of 9° C., and a pour point of less than -35° C. #10 is PETRO REP™ condensate having about 15% butanes, 46% pentanes, 19% hexanes and less than 1% aromatics as determined by gas chromatography. Run 95 is 100% FRACSOL™ well site operation fluid available from Trysol Canada Ltd. of Calgary, Alberta, Canada. FRACSOL™ is an aromatic rich petroleum distillate with the following properties;

    ______________________________________                                         Aromatics        63       LV %                                                 Reid Vapour Pressure                                                                            <1       kPa @ 37.8 deg. C.                                   Flashpoint (PMCC)                                                                               30       deg. C.                                              Flashpoint (COC) 35       deg. C.                                              Absolute Density 815      kg/m3 @ 15 deg. C.                                   API Gravity      42       deg. C.                                              Surface Tension (Oil to Air)                                                                    25       dynes/cm @ 22 deg. C.                                Interfacial Tension (Water to Oil)                                                              27       dynes/cm @ 22 deg. C.                                Cloud Point       8       deg. C.                                              Pour Point       -13      deg. C.                                              Aniline Point    56       deg. C.                                              ______________________________________                                    

90/10 is 90% of the 120° C. cut with 10% of a non-aromatic brominated non-fluorinated hydrocarbon such as dibromomethane. 90/10 Xy is 90% of the 150° C. cut described above with 10% of a non-aromatic brominated non-fluorinated hydrocarbon such as dibromomethane. 100 Xy is 100% of the 150° C. cut described above. 100 Xylene is pure xylene. Toluene is pure toluene. The oils from which some of the contaminants precipitated so far as known have the following composition: Sample 1. 8.26% asphaltene, 11.2% wax; Sample 4. 10% asphaltene; Sample 5. 23% asphaltene; Sample 22. 1.11% asphaltene, 4.7% wax; Sample 34c. 6.12% asphaltene, 2.9% wax; Sample 36. 3.43% asphaltene, 3.8% wax.

These results show that the formulation of the present invention provides comparable solvation properties to highly refined and expensive wax solvation products when applied to a variety of wells without specifically formulating the composition to the well formation.

By comparison with the product of the present invention, so far as known, the condensate available from other gas plants located in the Province of Alberta is not desirable for use as a wax and asphaltene removing fluid. Thus, for condensate from Amerada Hess (Bearberry), while the fluid is clear, showing low heavy ends, the aromatic content is too low by comparison with the light ends for a useful feedstock. Condensate from the Can-oxy Mazeppa plant is dark red from the plant, which becomes black when the lighter ends are removed, that is, when a C₇ + cut is taken, thus indicating the presence of undesirable heavy ends. Condensate from the Burnt Timber plant has too many heavy ends to work as a solvent, but may be formation compatible in some wells. Condensate from the Brazeau plant has too few aromatics, and too many waxes to be useful as a solvent. Condensate from Mobil Oil Lone Pine Creek has 6% xylene, which might suggest it is similar to the Jumping Pound feed (6.5% xylene). However, the relative lower percentage of lighter ends means that the concentration of xylene and other aromatics does not increase greatly if the lighter ends are removed in accordance with the principles of the invention. Consequently, the feed is not very useful as a solvent. Condensate from the Husky Oil Ram River plant has too many heavy ends, as indicated by its dark colour, and has too few aromatics to make it a useful feed for a solvent.

In the method of the invention, a C₅ + hydrocarbon feedstock is obtained in which feedstock the mass percentage of trimethylbenzene exceeds the mass percentage of decane as determined by gas chromatography; and substantially all hydrocarbons having 1, 2, 3, 4 and 5 carbon atoms are removed, thereby producing a residual fluid, effectively a C₇ + fluid. The fluid is applied to a well as follows.

For pumping or flowing wells, the well should be de-waxed before attempting to clean up the formation. To clean a pumping well, an amount of the fluid of the invention equal to about one half of the tubing volume should be circulated in the well with a bottomhole pump for about 24 hours. To clean the nearby well bore formation, a squeeze volume (1.0-1.5 m³ per meter of perforations) of the fluid according to the invention should be squeezed into the formation with a clean, formation compatible fluid. Preferably, the displacement fluid should be filtered to remove fines. After the fluid has been squeezed into the formation, the well should be shut in, and the fluid allowed to stand for 12 hours before putting the well back on pump.

To clean a partially plugged flowing well, a volume of the fluid according to the invention equal to one half of the tubing volume should be injected down the tubing string and allowed to soak for 24 hours. The well may then be placed back on production and tested.

To clean a completely plugged well, an attempt should be made to solubilize the plug by injecting a volume of the fluid according to the invention down the tubing string. If the plug can be solubilized, then the well should be allowed to soak for 24 hours and the well may be placed back on production and tested. If the plug cannot be solubilized, then the plug may be removed by such procedures as drilling or jetting with coiled tubing, using the fluid according to the invention as the jetting fluid. The well may then be placed back on production and evaluated.

To squeeze a flowing well in which the tubing is set in a packer, it is preferred to inject the fluid according to the invention directly through the perforations into the well bore using coiled tubing. This helps to prevent well fluid entrained solids from being re-injected into the well. If this procedure is not viable, then an attempt may be made to force the fluid according to the invention through the tubing into the formation with a clean formation compatible chase fluid. Care should be taken not to overflush the chase fluid into the formation.

To squeeze a flowing well in which the tubing is not set in a packer, it is preferred to squeeze a squeeze volume of the fluid according to the invention down the annulus to the perforations. The flowline should be kept open until the resident annulus fluid has been displaced up the tubing into the flowline. Typical squeeze volumes are 1.0-1.5 m³ of the fluid according to the invention per meter of perforations. Once the fluid is in the annulus, the tubing valve may be closed and the fluid squeezed into the formation with a clean formation compatible fluid (which should not be overflushed). In either case (with or without the tubing set in a packer), the well may be shut in, allowed to soak and after 24 hours or so, placed back on production and tested.

If a flowing well does not flow after treatment, it may be desirable at that point to swab the well.

The formulation of the present invention, identified by Trisol Inc.'s tradename WAXSOL is preferably pumped into the well at below fracturing pressures. Pumping is carried out at ambient temperature. As known in the art, since the formulation of the invention is aromatic rich, contact with elastomeric components in the well should be minimized. For removal of the formulation of the invention from the well, high (maximum) pump speeds are recommended to aid in preventing the plugging of downhole pumps by release of fines and scale from downhole wax as it is dissolved.

A person skilled in the art could make immaterial modifications to the invention described and claimed in this patent without departing from the essence of the invention.

An example of feedstock which fits the criteria outlined for asphaltene solvating capabilities include the condensate available at Caroline, Alberta, Canada. A gas chromatograph profile (graphic and numerical) of the feedstock is attached as FIG. 3 with the TMB peak shown at 10 and the n-decane peak shown at 12. A numerical representation of the chromatograph of FIG. 3 is presented in Table 4.

                  TABLE 4                                                          ______________________________________                                         SHELL CAROLINE                                                                 Ceiling                  Carbon                                                Range                    Number                                                                               Mol.  Mass                                      (C)   PT      Component  %     %     %     Volume                              ______________________________________                                               -161.7  Methane    C1    0.00  0.00  0.00                                      -88.9   Ethane     C2    0.00  0.00  0.00                                      -42.2   Propane    C3    0.00  0.00  0.00                                      -11.7   iso-Butane C4    0.00  0.00  0.00                                      -0.6    n-Butane   C4    0.00  0.00  0.00                                      27.8    iso-Pentane                                                                               C5    0.00  0.00  0.00                                      36.1    n-Pentane  C5    0.00  0.00  0.00                                 36.1 -68.9   n-Hexanes  C6    5.16  3.80  4.52                                 68.9 -98.3   Heptanes   C7    8.61  7.38  8.43                                 98.3 -125.6  Octanes    C8    7.59  7.41  8.28                                125.6 -150.6  Nonanes    C9    2.85  3.13  3.41                                150-6 -173.9  Decanes    C10   8.28  10.08 10.79                               173.9 -196.1  Undecanes  C11   3.88  5.18  5.48                                196-1 -215.0  Dodecanes  C12   1.78  2.59  2.71                                215.0 -235.0  Tridecanes C13   0.90  1.42  1.47                                235.0 -252.0  Tetradecanes                                                                              C14   0.62  1.05  1.07                                252.2 -270.6  Pentadecanes                                                                              C15   0.60  1.09  1.10                                270.6 -287.8  Hexadecanes                                                                               C16   0.54  1.05  1.06                                287.8 -302.8  Heptadecanes                                                                              C17   0.46  0.95  0.96                                302.8 -317.2  Octadecanes                                                                               C18   1.16  2.52  2.51                                317.2 -330.0  Nonadecanes                                                                               C19   1.24  2.85  2.83                                330.0 -344.4  Eicosanes  C20   0.19  0.46  0.46                                344.4 -357.2  Heneicosanes                                                                              C21   0.03  0.09  0.08                                357.2 -369.4  Docosanes  C22   0.00  0.01  0.01                                369.4 -380.0  Tricosanes C23   0.00  0.00  0.00                                380.0 -391.1  Tetracosanes                                                                              C24   0.00  0.00  0.00                                391.1 -401.7  Pentacosanes                                                                              C25   0.00  0.00  0.00                                401.7 -412.2  Hexacosanes                                                                               C26   0.00  0.00  0.00                                412.2 -422.2  Heptacosanes                                                                              C27   0.00  0.00  0.00                                422.2 -431.7  Octacosanes                                                                               C28   0.00  0.00  0.00                                431.7 -441.1  Nonacosanes                                                                               C29   0.00  0.00  0.00                                441.1 PLUS    Triacontanes                                                                                C30+                                                                               0.00  0.00  0.00                                      80      Benzene    C6H6  0.80  0.54  0.47                                      110.6   Toluene    C7H8  12.29 9.68  8.74                                110.6 -138.9  Ethyl Benzene                                                                             C8H1O 23.19 21.04 19.04                                             mtp-xylene                                                             144.4   o-Xylene   C8H1O 5.85  5.31  4.67                                      168.9   1,2,4-tri- C9H12 5.55  5.70  5.12                                              methylbenzene                                                          48.9    Cyclopentane                                                                              C5H1O 0.00  0.00  0.00                                      72.2    Methylcyclo-                                                                              C6H12 1.45  1.05  1.09                                              pentane                                                                81.1    Cyclohexane                                                                               C6H12 1.66  1.20  1.20                                      101.1   Methylcyclo-                                                                              C7H14 5.28  4.43  4.50                                              hexane                                                                   TOTAL        100.00  100.00  100.00                                    ______________________________________                                    

Only simple aromatics are quantified and listed on this table. Total aromatic content, including more complex aromatics, have been analyzed by supercritical fluid chromatography at greater than 40 % mole fraction.

A further example of a feedstock which fits the criteria outlined for asphaltene solvating capabilities and which may be the most preferred includes the condensate available at the Hanlan Gas Plant in Alberta, Canada. A gas chromatograph profile (graphic) of the feedstock is attached as FIG. 4 with the TMB peak shown at 10 and the n-decane shown at 12.

Obvious modifications may be made to the invention described here without departing from the essence of the invention. 

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:
 1. A method of treating a well with a wax and asphaltene solvating oil well site operation fluid, the method comprising the steps of:obtaining a hydrocarbon feedstock that has been produced directly from an oil or gas bearing formation, the hydrocarbon feedstock containing at least hydrocarbons having eight, nine, ten, eleven and twelve carbon atoms, including trimethylbenzene and n-decane; performing a gas chromatographic analysis on the feedstock to verify that the mass percentage of trimethylbenzene exceeds the mass percentage of n-decane; and subsequently applying the feedstock or a residual fluid derived from the feedstock to an oil or gas well having contaminants selected from the group consisting of wax and asphaltenes.
 2. The method of claim 1 in which the hydrocarbon feedstock further includes at least hydrocarbons selected from the group consisting of 1, 2, 3, 4 and 5 carbon atom hydrocarbons and the method further including removing substantially all of the selected hydrocarbons having 1, 2, 3, 4 and 5 carbon atoms from the feedstock, thereby producing a residual fluid derived from the feedstock, which residual fluid is applied to the oil or gas well.
 3. The method of claim 2 in which the residual fluid is allowed to stand in the well for at least 12 hours and further including recovering the residual fluid from the well.
 4. The method of claim 3 in which the hydrocarbon feedstock further includes at least hydrocarbons selected from the group consisting of hydrocarbons having 6 and 7 carbon atoms and the method further comprising:refining the residual fluid to remove substantially all of the selected hydrocarbons having 6 or 7 carbon atoms.
 5. The method of claim 1 further comprising:refining the residual fluid to reduce mass fraction of the residual fluid having more than 16 atoms.
 6. A method of treating an oil or gas well with an oil well site operation fluid to remove asphaltene and wax from the well, the method comprising the steps of:obtaining a residual C₅ + hydrocarbon fluid derived from a hydrocarbon feedstock, the hydrocarbon feedstock and the residual C₅ + hydrocarbon fluid containing a complex mixture of aromatics in which feedstock the mass percentage of trimethylbenzene exceeds the mass percentage of n-decane as determined by gas chromatography; and applying the residual C₅ + hydrocarbon fluid to an oil or gas well having contaminants.
 7. The method of claim 6 in which the residual C₅ + hydrocarbon fluid includes greater than 2% mass fraction hydrocarbons having more than 16 carbon atoms and the method further comprising:before applying the residual C₅ + hydrocarbon fluid to an oil or gas well, refining the residual C₅ + hydrocarbon fluid to reduce the mass fraction of the hydrocarbons having more than 16 carbon atoms.
 8. The method of claim 6 in which the residual C₅ + hydrocarbon fluid further includes hydrocarbons selected from the group consisting of hydrocarbons with 6 or 7 carbon atoms and the method further comprising:before applying the residual C₅ + hydrocarbon fluid to an oil or gas well, refining the residual C₅ + hydrocarbon fluid to remove substantially all of the selected hydrocarbons having 6 or 7 carbon atoms.
 9. The method of claim 8 in which the residual C₅ + hydrocarbon fluid is allowed to stand in the well for at lest 12 hours, further comprising subsequently recovering the residual C₅ + hydrocarbon fluid from the well.
 10. The method of claim 9 in which pressure is applied to the residual C₅ + hydrocarbon fluid in the well.
 11. The method of claim 6 in which the residual C₅ + hydrocarbon fluid is allowed to stand in the well for at least 12 hours, further comprising subsequently recovering the residual C₅ + hydrocarbon fluid from the well.
 12. The method of claim 6 in which pressure is applied to the residual C₅ + hydrocarbon fluid in the well.
 13. A method of treating an oil or gas well with an oil well site operation fluid to remove asphaltene and wax from the well, the method comprising the steps of:obtaining a hydrocarbon fluid that has been produced directly from an oil or gas bearing formation, the hydrocarbon fluid containing at least hydrocarbons having eight, nine, ten, eleven and twelve carbon atoms, including trimethylbenzene and n-decane, and containing a complex mixture of aromatics, in which fluid the mass percentage of trimethylbenzene exceeds the mass percentage of n-decane as determined by gas chromatography; and applying the hydrocarbon fluid to an oil or gas well having contaminants.
 14. The method of claim 13 in which the hydrocarbon fluid has greater than 2% mass fraction hydrocarbons having more than 16 carbon atoms and the method further comprising the step of:before applying the hydrocarbon fluid to a well, refining the hydrocarbon fluid to reduce mass fraction of the hydrocarbon fluid having more than 16 carbon atoms.
 15. The method of claim 13 in which the hydrocarbon fluid is allowed to stand in the well for at least 12 hours, further comprising susequently recovering the hydrocarbon fluid from the well.
 16. The method of claim 13 in which pressure is applied to the hydrocarbon fluid in the well.
 17. The method of claim 13 in which the hydrocarbon fluid further includes hydrocarbons selected from the group consisting of the hydrocarbons having 1, 2, 3, 4 and 5 carbon atoms and further comprising the step of:before applying the hydrocarbon fluid to a well, refining the hydrocarbon fluid to reduce the selected C₁ to C₅ hydrocarbon content to cumulatively less than 5% mass fraction.
 18. The method of claim 13 in which the hydrocarbon fluid further includes hydrocarbons selected from the group consisting of the hydrocarbons having 1, 2, 3, 4, 5 and 6 carbon atoms and further comprising the step of:before applying the hydrocarbon fluid to a well, refining the hydrocarbon fluid to reduce the selected C₁ to C₆ hydrocarbon content to cumulatively less than 5% mass fraction.
 19. The method of claim 13 in which the hydrocarbon fluid further includes hydrocarbons selected from the group consisting of hydrocarbons having 1, 2, 3, 4, 5, 6 and 7 carbon atoms and further comprising the step of:before applying the hydrocarbon fluid to a well, refining the hydrocarbon fluid to reduce the selected C₁ to C₇ hydrocarbon content to cumulatively less than 5% mass fraction.
 20. A method of treating an oil or gas well with an oil well site operation fluid to remove asphaltene and wax contaminants from the well, the method comprising the steps of:withdrawing a hydrocarbon feedstock from an oil or gas bearing formation, the feedstock containing at least C₈ through C₁₂ hydrocarbons and including a complex mixture of aromatics including trimethylenzene and n-decane, the feedstock including a greater mass percentage of of trimethylbenzene than n-decane; removing C₁ through C₅ hydrocarbons from the withdrawn feedstock to produce a C₈ through C₁₂ hyrdrocarbon residual; and injecting the C₈ through C₁₂ hydrocarbon residual into the oil or gas well to solvate the asphaltene and wax contaminants.
 21. A method of treating an oil or gas well with an oil well site operation fluid to remove asphaltene and wax contaminants from the well, the method comprising the steps of:withdrawing a hydrocarbon feedstock from an oil or gas bearing formation, the feedstock containing at least C₈ through C₁₂ hydrocarbons and including a complex mixture of aromatics including trimethylbenzene and n-decane, the feedstock including a greater mass percentage of trimetylbenzene than n-decane; removing C₁ through C₅ hydrocarbons from the withdrawn feedstock to produce a C₈ throught C₁₂ hydrocarbon residual; and injecting the C₈ through C₁₂ hydrocarbon residual into the oil or gas well to solvate at least 63% of the asphaltene and wax contaminants. 